In industry, motors generally are used for generating power, and gear reducers are used as a means for transmission shifting. A motor combines with a gear reducer for improving a torque of the motor or reducing the speed. The motor and the gear reducer must be matched based on work load, working speed, and maintaining motor operation at the most efficient operating point, in order to achieve better operating characteristics for the motor. A machine system can be divided into three main sub-systems, namely the power source, the transmission, and the working machine to transform the power into mechanical energy to achieve the desired functions. The electric motors and gear mechanisms are wildly used as power sources and transmissions, respectively. However they are designed separately. Traditionally, in order to combine the motors and gear trains, the couplings and other power transmission elements are used. And, the disadvantages of such design are longer power transmitting path, incompact space, and extra elements.
It is noted that cogging torque is the torque due to the interaction between the stator and the rotor core in a motor. The n-th harmonic components that cause the cogging torque are given by:
            T      n        =          i      ⁢              T                  gcd          ⁡                      (                          P              ,              T                        )                                ,      i    =    1    ,  2  ,  3  ,  …
where gcd(P,T) is the greatest common divisor of the number of magnet poles P and the number of integrated gear-teeth T It is apparent that the order of the harmonic components that dominate the cogging torque is directly related to the number of gear teeth on the rotor and the number of magnet poles in a traditional AC motor.
FIG. 1 is a perspective view of a traditional AC motor 11 and a traditional gear reducer 12. The traditional AC motor 11 and the traditional gear reducer 12 are separated, and connected by the Intermediary mechanical components. Such as couplings or power-transmitting elements, are further employed for transmitting motion and/or power from the electric motor to the gear reducer. An output shaft 111 of the motor 11 is engaged with an input member 121 of the gear reducer 12 so that the output torque of the motor 11 is delivered to the gear reducer 12.
However, it suffers from significant disadvantages, such as the use of couplings or power-transmitting elements, which is the primary failure source and increases the maintenance complexity and manufacturing costs. The additional mechanical loss caused by the friction of intermediary components results in undesirable low efficiency. In addition, the output torque of the motor 11 is delivered to the gear reducer 12 through the coupling, and a path of the power transmission between the motor 11 and the gear reducer 12 is longer, and a friction of the coupling losses additional mechanical energy, resulting in lower efficiency. The motor 11 and the gear reducer 12 are independently design and manufactured. The transmission components, racks, and lock parts are provided to combine the motor 11 and the gear reducer 12, which increases manufacturing and maintenance costs, so that the accuracy of the system is reduced. Moreover, the volume of the motor 11 and the gear reducer 12 is large and difficult to change so that the installation space can't be planted.
As a result, it is necessary to provide a developed alternating current (AC) motor to solve the problems existing in the conventional technologies, as described above.